Damned if you do & Damned if you don't. But can you imagine the damage Israel would do to the worlds economies by a pre-emptive strike. The other side of that option is Israel isn't huge so like they say one nuke to them pretty much spoils the whole nation with radiation. We Americans don't have any desire to war with Iran. No need, no justification no right to war with them. No money either. Look at India/pakistan/N Korea, they have nukes and have not used them. Why? because they know they are defensive weapons and if attacked they can use them. Iran is no different I dare say. Israel has Nukes and thats a fact so you can't have it both ways and than cry foul when the other independent nations do the same for the same reasons.
Israeli troops shoot, injure Palestinian crossing Gaza border fence (Haaretz)
from the article: General Dempsey is 'complicit' in goading Israel to attack Iran